First of all, thank you very much for taking the time to post and for your kind words, I really do appreciate them! :-)

Being able to understand and use both systems (GNU and S/MIME) will indeed be of help and help you greatly you for your future exchanges.

While I of course have no insider knowledge about what happens at Apple, I would think that issuing certificates is so heavily linked to country-specific legal issues that implementing such a feature would be relatively difficult. This is of course just a thought and (who knows), a system similar to the one you describe might be in the works...